Foreign object detection using heat sensitive material and inductive sensing

ABSTRACT

In certain aspects, a method and apparatus for detecting foreign objects using heat sensitive material and inductive sensing is disclosed. In certain aspects, a foreign object detection system includes a heat sensing system comprising a heat sensitive material having a property configured to change as a function of temperature. The foreign object detection system further includes an inductive sensing system comprising one or more sense coils, wherein a change in an electrical characteristic of the one or more sense coils is indicative of presence of a foreign object. The foreign object detection system further includes a controller coupled to the heat sensing system and the inductive sensing system, wherein the controller is configured to determine presence of the foreign object based on at least one of a measure of the property of the heat sensitive material or a measure of the electrical characteristic of the one or more sense coils.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/444,714, filed Jan. 10, 2017 and U.S. ProvisionalPatent Application No. 62/457,462, filed Feb. 10, 2017. The content ofeach of which is hereby incorporated by reference in its entirety.

FIELD

This application is generally related to wireless charging powertransfer applications, and specifically to a method and apparatus fordetecting foreign objects using heat sensitive material and inductivesensing.

BACKGROUND

Wireless power transfer systems (e.g., inductive charging systems forelectric vehicles) may include a ground-based wireless power transmitter(e.g., a base pad, base wireless charging system, or some other wirelesspower transfer device including a coupler (e.g., base coupler))configured to emit a wireless power field to a wireless power receiver(e.g., a vehicle pad, an electric vehicle wireless charging unit, orsome other wireless power receiving device including a coupler (e.g.,vehicle coupler)) configured to receive the wireless power field on thebottom of the vehicle. In such wireless power transfer systems, thespace between the wireless power transmitter on the ground and thewireless power receiver on the vehicle may be open and accessible byforeign objects. For example, foreign objects may accidentally orintentionally be positioned in the space between the wireless powertransmitter and the wireless power receiver. Where the foreign object isconducting and/or ferromagnetic (e.g., a metallic object, such as apaper clip, screw, etc.)), when the foreign object is exposed to thewireless charging field between the wireless power transmitter and thewireless power receiver, it may reach high temperatures (e.g., over 200degrees C.), for example due to eddy current and hysteresis effectscaused by the wireless charging field, if flux density levels exceedcertain critical levels. The high temperatures the foreign object maypotentially reach may damage the wireless power transmitter. Forexample, the foreign object may sit on the wireless power transmitterand cause portions of the wireless power transmitter to melt or burn, ormay itself melt into the wireless power transmitter. Further, detectingthe foreign object using certain foreign object detection (FOD)techniques may not be feasible, such as due to the object being smalland difficult to detect, or may be too costly. Accordingly, a method andapparatus for detecting foreign objects as described is desirable.

SUMMARY

In certain aspects, a foreign object detection system is disclosed. Theforeign object detection system includes a heat sensing systemcomprising a heat sensitive material having a property configured tochange as a function of temperature. The foreign object detection systemfurther includes an inductive sensing system comprising one or moresense coils, wherein a change in an electrical characteristic of the oneor more sense coils is indicative of presence of a foreign object. Theforeign object detection system further includes a controller coupled tothe heat sensing system and the inductive sensing system, wherein thecontroller is configured to determine presence of the foreign objectbased on at least one of a measure of the property of the heat sensitivematerial or a measure of the electrical characteristic of the one ormore sense coils.

In certain aspects, a method for controlling a foreign object detectionsystem is disclosed. The method includes determining a change in aproperty of a heat sensitive material. The method further includesdetermining a change in an electrical characteristic of one or moresense coils. The method further includes determining presence of aforeign object based on at least one of the determined change in theproperty of the heat sensitive material or the determined change in theelectrical characteristic of one or more sense coils.

In certain aspects, a foreign object detection system is disclosed. Theforeign object detection system includes first means for sensingpresence of a foreign object based on temperature. The foreign objectdetection system further includes second means for sensing presence ofthe foreign object based on inductance. The foreign object detectionsystem further includes means for determining presence of the foreignobject based on at least one of the first means for sensing or thesecond means for sensing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless power transfer system for charging anelectric vehicle, in accordance with some implementations.

FIG. 2 is a schematic diagram of exemplary components of the wirelesspower transfer system of FIG. 1.

FIG. 3 is a functional block diagram showing exemplary components of thewireless power transfer system of FIG. 1.

FIG. 4A illustrates an example of an enclosure for a wireless powertransfer pad, in accordance with an illustrative aspect.

FIG. 4B illustrates an example of an enclosure for a wireless powertransfer pad, in accordance with an illustrative aspect.

FIG. 4C illustrates an example of an enclosure for a wireless powertransfer pad, in accordance with an illustrative aspect.

FIG. 4D illustrates an example of an enclosure for a wireless powertransfer pad, in accordance with an illustrative aspect.

FIG. 5 illustrates an example of a heat sensitive layer, in accordancewith an illustrative aspect.

FIG. 6 illustrates an example of a circuit corresponding to the heatsensitive layer of FIG. 5, in accordance with an illustrative aspect.

FIG. 7 illustrates an example of a heat sensitive layer, in accordancewith an illustrative aspect.

FIG. 8 illustrates an example of a heat sensitive layer, in accordancewith an illustrative aspect.

FIGS. 9A and 9B illustrate exemplary aspects of a selective heatsensitive array, in accordance with an illustrative aspect.

FIG. 10 illustrates an example of a circuit corresponding to a heatsensitive layer, in accordance with an illustrative aspect.

FIG. 11 is a circuit diagram illustrating an example of an inductiveforeign object detector, in accordance with an illustrative aspect.

FIG. 12A illustrates an example of a bifilar inductive sense coil usinga heat sensitive material, in accordance with an illustrative aspect.

FIG. 12B illustrates an example of a bifilar inductive sense coilembedded in a heat sensitive layer, in accordance with an illustrativeaspect.

FIG. 12C illustrates another example of a bifilar inductive sense coilwith a heat sensitive layer between the two coil windings, in accordancewith an illustrative aspect.

FIG. 13A is a circuit diagram illustrating an example of a foreignobject detector combining inductive sensing and heat sensing, inaccordance with an illustrative aspect.

FIG. 13B is a circuit diagram illustrating another example of a foreignobject detector combining inductive sensing and heat sensing, inaccordance with an illustrative aspect.

FIG. 14 illustrates example operations for performing combined inductivesensing and heat sensing for foreign object detection, in accordancewith an illustrative aspect.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary implementations andis not intended to represent the only implementations in which theinvention may be practiced. The term “exemplary” used throughout thisdescription means “serving as an example, instance, or illustration,”and should not necessarily be construed as preferred or advantageousover other exemplary implementations. The detailed description includesspecific details for the purpose of providing a thorough understandingof the exemplary implementations. In some instances, some devices areshown in block diagram form.

Wirelessly transferring power may refer to transferring any form ofenergy associated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield) may be received, captured by, or coupled by a “receiving coil” toachieve power transfer.

An electric vehicle is used herein to describe a remote system, anexample of which is a vehicle that includes, as part of its locomotioncapabilities, electrical power derived from a chargeable energy storagedevice (e.g., one or more rechargeable electrochemical cells or othertype of battery). As non-limiting examples, some electric vehicles maybe hybrid electric vehicles that include, besides electric motors, atraditional combustion engine for direct locomotion or to charge thevehicle's battery. Other electric vehicles may draw all locomotionability from electrical power. An electric vehicle is not limited to anautomobile and may include motorcycles, carts, scooters, and the like.By way of example and not limitation, a remote system is describedherein in the form of an electric vehicle (EV). Furthermore, otherremote systems that may be at least partially powered using a chargeableenergy storage device are also contemplated (e.g., electronic devicessuch as personal computing devices and the like).

FIG. 1 is a diagram of an exemplary wireless power transfer system 100for charging an electric vehicle, in accordance with some exemplaryimplementations. The wireless power transfer system 100 enables chargingof an electric vehicle 112 while the electric vehicle 112 is parked soas to efficiently couple with a base wireless charging system 102 a.Spaces for two electric vehicles are illustrated in a parking area to beparked over corresponding base wireless charging systems 102 a and 102b. In some implementations, a local distribution center 130 may beconnected to a power backbone 132 and configured to provide analternating current (AC) or a direct current (DC) supply through a powerlink 110 to the base wireless charging systems 102 a and 102 b. Each ofthe base wireless charging systems 102 a and 102 b also includes a basecoupler 104 a and 104 b, respectively, for wirelessly transferringpower. In some other implementations (not shown in FIG. 1), basecouplers 104 a or 104 b may be stand-alone physical units and are notpart of the base wireless charging system 102 a or 102 b.

The electric vehicle 112 may include a battery unit 118, an electricvehicle coupler 116, and an electric vehicle wireless charging unit 114.The electric vehicle wireless charging unit 114 and the electric vehiclecoupler 116 constitute the electric vehicle wireless charging system. Insome diagrams shown herein, the electric vehicle wireless charging unit114 is also referred to as the vehicle charging unit (VCU). The electricvehicle coupler 116 may interact with the base coupler 104 a forexample, via a region of the electromagnetic field generated by the basecoupler 104 a.

In some exemplary implementations, the electric vehicle coupler 116 mayreceive power when the electric vehicle coupler 116 is located in anelectromagnetic field produced by the base coupler 104 a. The field maycorrespond to a region where energy output by the base coupler 104 a maybe captured by the electric vehicle coupler 116. For example, the energyoutput by the base coupler 104 a may be at a level sufficient to chargeor power the electric vehicle 112. In some cases, the field maycorrespond to a “near-field” of the base coupler 104 a. The near-fieldmay correspond to a region in which there are strong reactive fieldsresulting from the currents and charges in the base coupler 104 a thatdo not radiate power away from the base coupler 104 a. In some cases thenear-field may correspond to a region that is within about ½π of awavelength of the a frequency of the electromagnetic field produced bythe base coupler 104 a distant from the base coupler 104 a, as will befurther described below.

Local distribution center 130 may be configured to communicate withexternal sources (e.g., a power grid) via a communication backhaul 134,and with the base wireless charging system 102 a via a communicationlink 108.

In some implementations the electric vehicle coupler 116 may be alignedwith the base coupler 104 a and, therefore, disposed within a near-fieldregion simply by the electric vehicle operator positioning the electricvehicle 112 such that the electric vehicle coupler 116 is sufficientlyaligned relative to the base coupler 104 a. Alignment may be consideredsufficient when an alignment error has fallen below a tolerable value.In other implementations, the operator may be given visual and/orauditory feedback to determine when the electric vehicle 112 is properlyplaced within a tolerance area for wireless power transfer. In yet otherimplementations, the electric vehicle 112 may be positioned by anautopilot system, which may move the electric vehicle 112 until thesufficient alignment is achieved. This may be performed automaticallyand autonomously by the electric vehicle 112 with or without driverintervention. This may be possible for an electric vehicle 112 that isequipped with a servo steering, radar sensors (e.g., ultrasonicsensors), and intelligence for safely maneuvering and adjusting theelectric vehicle. In still other implementations, the electric vehicle112 and/or the base wireless charging system 102 a may havefunctionality for mechanically displacing and moving the couplers 116and 104 a, respectively, relative to each other to more accuratelyorient or align them and develop sufficient and/or otherwise moreefficient coupling there between.

The base wireless charging system 102 a may be located in a variety oflocations. As non-limiting examples, some suitable locations include aparking area at a home of the electric vehicle 112 owner, parking areasreserved for electric vehicle wireless charging modeled afterconventional petroleum-based filling stations, and parking lots at otherlocations such as shopping centers and places of employment.

Charging electric vehicles wirelessly may provide numerous benefits. Forexample, charging may be performed automatically, virtually withoutdriver intervention or manipulation thereby improving convenience to auser. There may also be no exposed electrical contacts and no mechanicalwear out, thereby improving reliability of the wireless power transfersystem 100. Safety may be improved since manipulations with cables andconnectors may not be needed and there may be no cables, plugs, orsockets to be exposed to moisture in an outdoor environment. Inaddition, there may also be no visible or accessible sockets, cables, orplugs, thereby reducing potential vandalism of power charging devices.Further, since the electric vehicle 112 may be used as distributedstorage devices to stabilize a power grid, a convenient docking-to-gridsolution may help to increase availability of vehicles forvehicle-to-grid (V2G) operation.

The wireless power transfer system 100 as described with reference toFIG. 1 may also provide aesthetical and non-impedimental advantages. Forexample, there may be no charge columns and cables that may beimpedimental for vehicles and/or pedestrians.

As a further explanation of the vehicle-to-grid capability, the wirelesspower transmit and receive capabilities may be configured to bereciprocal such that either the base wireless charging system 102 a cantransmit power to the electric vehicle 112 or the electric vehicle 112can transmit power to the base wireless charging system 102 a. Thiscapability may be useful to stabilize the power distribution grid byallowing electric vehicles 112 to contribute power to the overalldistribution system in times of energy shortfall caused by over demandor shortfall in renewable energy production (e.g., wind or solar).

FIG. 2 is a schematic diagram of exemplary components of a wirelesspower transfer system 200 similar to that previously discussed inconnection with FIG. 1, in accordance with some exemplaryimplementations. The wireless power transfer system 200 may include abase resonant circuit 206 including a base coupler 204 having aninductance L1. The wireless power transfer system 200 further includesan electric vehicle resonant circuit 222 including an electric vehiclecoupler 216 having an inductance L2. Implementations described hereinmay use capacitively loaded conductor loops (i.e., multi-turn coils)forming a resonant structure that is capable of efficiently couplingenergy from a primary structure (transmitter) to a secondary structure(receiver) via a magnetic or electromagnetic near-field if both thetransmitter and the receiver are tuned to a common resonant frequency.The coils may be used for the electric vehicle coupler 216 and the basecoupler 204. Using resonant structures for coupling energy may bereferred to as “magnetically coupled resonance,” “electromagneticallycoupled resonance,” and/or “resonant induction.” The operation of thewireless power transfer system 200 will be described based on powertransfer from a base coupler 204 to an electric vehicle 112 (not shown),but is not limited thereto. For example, as discussed above, energy maybe also transferred in the reverse direction.

With reference to FIG. 2, a power supply 208 (e.g., AC or DC) suppliespower PSDC to the base power converter 236 as part of the base wirelesspower charging system 202 to transfer energy to an electric vehicle(e.g., electric vehicle 112 of FIG. 1). The base power converter 236 mayinclude circuitry such as an AC-to-DC converter configured to convertpower from standard mains AC to DC power at a suitable voltage level,and a DC-to-low frequency (LF) converter configured to convert DC powerto power at an operating frequency suitable for wireless high powertransfer. The base power converter 236 supplies power P1 to the baseresonant circuit 206 including tuning capacitor C1 in series with basecoupler 204 to emit an electromagnetic field at the operating frequency.The series-tuned resonant circuit 206 should be construed as exemplary.In another implementation, the capacitor C1 may be coupled with the basecoupler 204 in parallel. In yet other implementations, tuning may beformed of several reactive elements in any combination of parallel orseries topology. The capacitor C1 may be provided to form a resonantcircuit with the base coupler 204 that resonates substantially at theoperating frequency. The base coupler 204 receives the power P1 andwirelessly transmits power at a level sufficient to charge or power theelectric vehicle. For example, the level of power provided wirelessly bythe base coupler 204 may be on the order of kilowatts (kW) (e.g.,anywhere from 1 kW to 110 kW, although actual levels may be or higher orlower).

The base resonant circuit 206 (including the base coupler 204 and tuningcapacitor C1) and the electric vehicle resonant circuit 222 (includingthe electric vehicle coupler 216 and tuning capacitor C2) may be tunedto substantially the same frequency. The electric vehicle coupler 216may be positioned within the near-field of the base coupler and viceversa, as further explained below. In this case, the base coupler 204and the electric vehicle coupler 216 may become coupled to one anothersuch that power may be transferred wirelessly from the base coupler 204to the electric vehicle coupler 216. The series capacitor C2 may beprovided to form a resonant circuit with the electric vehicle coupler216 that resonates substantially at the operating frequency. Theseries-tuned resonant circuit 222 should be construed as beingexemplary. In another implementation, the capacitor C2 may be coupledwith the electric vehicle coupler 216 in parallel. In yet otherimplementations, the electric vehicle resonant circuit 222 may be formedof several reactive elements in any combination of parallel or seriestopology. Element k(d) represents the mutual coupling coefficientresulting at coil separation d. Equivalent resistances Req,1 and Req,2represent the losses that may be inherent to the base and electricvehicle couplers 204 and 216 and the tuning (anti-reactance) capacitorsC1 and C2, respectively. The electric vehicle resonant circuit 222,including the electric vehicle coupler 216 and capacitor C2, receivesand provides the power P2 to an electric vehicle power converter 238 ofan electric vehicle charging system 214.

The electric vehicle power converter 238 may include, among otherthings, a LF-to-DC converter configured to convert power at an operatingfrequency back to DC power at a voltage level of the load 218 that mayrepresent the electric vehicle battery unit. The electric vehicle powerconverter 238 may provide the converted power PLDC to the load 218. Thepower supply 208, base power converter 236, and base coupler 204 may bestationary and located at a variety of locations as discussed above. Theelectric vehicle load 218 (e.g., the electric vehicle battery unit),electric vehicle power converter 238, and electric vehicle coupler 216may be included in the electric vehicle charging system 214 that is partof the electric vehicle (e.g., electric vehicle 112) or part of itsbattery pack (not shown). The electric vehicle charging system 214 mayalso be configured to provide power wirelessly through the electricvehicle coupler 216 to the base wireless power charging system 202 tofeed power back to the grid. Each of the electric vehicle coupler 216and the base coupler 204 may act as transmit or receive couplers basedon the mode of operation.

While not shown, the wireless power transfer system 200 may include aload disconnect unit (LDU) (not shown) to safely disconnect the electricvehicle load 218 or the power supply 208 from the wireless powertransfer system 200. For example, in case of an emergency or systemfailure, the LDU may be triggered to disconnect the load from thewireless power transfer system 200. The LDU may be provided in additionto a battery management system for managing charging to a battery, or itmay be part of the battery management system.

Further, the electric vehicle charging system 214 may include switchingcircuitry (not shown) for selectively connecting and disconnecting theelectric vehicle coupler 216 to the electric vehicle power converter238. Disconnecting the electric vehicle coupler 216 may suspend chargingand also may change the “load” as “seen” by the base wireless powercharging system 202 (acting as a transmitter), which may be used to“cloak” the electric vehicle charging system 214 (acting as thereceiver) from the base wireless charging system 202. The load changesmay be detected if the transmitter includes a load sensing circuit.Accordingly, the transmitter, such as the base wireless charging system202, may have a mechanism for determining when receivers, such as theelectric vehicle charging system 214, are present in the near-fieldcoupling mode region of the base coupler 204 as further explained below.

As described above, in operation, during energy transfer towards anelectric vehicle (e.g., electric vehicle 112 of FIG. 1), input power isprovided from the power supply 208 such that the base coupler 204generates an electromagnetic field for providing the energy transfer.The electric vehicle coupler 216 couples to the electromagnetic fieldand generates output power for storage or consumption by the electricvehicle 112. As described above, in some implementations, the baseresonant circuit 206 and electric vehicle resonant circuit 222 areconfigured and tuned according to a mutual resonant relationship suchthat they are resonating nearly or substantially at the operatingfrequency. Transmission losses between the base wireless power chargingsystem 202 and electric vehicle charging system 214 are minimal when theelectric vehicle coupler 216 is located in the near-field coupling moderegion of the base coupler 204 as further explained below.

As stated, an efficient energy transfer occurs by transferring energyvia a magnetic near-field rather than via electromagnetic waves in thefar field, which may involve substantial losses due to radiation intothe space. When in the near-field, a coupling mode may be establishedbetween the transmit coupler and the receive coupler. The space aroundthe couplers where this near-field coupling may occur is referred toherein as a near-field coupling mode region.

While not shown, the base power converter 236 and the electric vehiclepower converter 238 if bidirectional may both include, for the transmitmode, an oscillator, a driver circuit such as a power amplifier, afilter and matching circuit, and for the receive mode a rectifiercircuit. The oscillator may be configured to generate a desiredoperating frequency, which may be adjusted in response to an adjustmentsignal. The oscillator signal may be amplified by a power amplifier withan amplification amount responsive to control signals. The filter andmatching circuit may be included to filter out harmonics or otherunwanted frequencies and match the impedance as presented by theresonant circuits 206 and 222 to the base and electric vehicle powerconverters 236 and 238, respectively. For the receive mode, the base andelectric vehicle power converters 236 and 238 may also include arectifier and switching circuitry.

The electric vehicle coupler 216 and base coupler 204 as describedthroughout the disclosed implementations may be referred to orconfigured as “conductor loops”, and more specifically, “multi-turnconductor loops” or coils. The base and electric vehicle couplers 204and 216 may also be referred to herein or be configured as “magnetic”couplers. The term “coupler” is intended to refer to a component thatmay wirelessly output or receive energy for coupling to another“coupler.”

As discussed above, efficient transfer of energy between a transmitterand receiver occurs during matched or nearly matched resonance between atransmitter and a receiver. However, even when resonance between atransmitter and receiver are not matched, energy may be transferred at alower efficiency.

A resonant frequency may be based on the inductance and capacitance of aresonant circuit (e.g. resonant circuit 206) including a coupler (e.g.,the base coupler 204 and capacitor C2) as described above. As shown inFIG. 2, inductance may generally be the inductance of the coupler,whereas, capacitance may be added to the coupler to create a resonantstructure at a desired resonant frequency. Accordingly, for larger sizecouplers using larger diameter coils exhibiting larger inductance, thevalue of capacitance needed to produce resonance may be lower.Inductance may also depend on a number of turns of a coil. Furthermore,as the size of the coupler increases, coupling efficiency may increase.This is mainly true if the size of both base and electric vehiclecouplers increase. Furthermore a resonant circuit including a couplerand tuning capacitor may be designed to have a high quality (Q) factorto improve energy transfer efficiency. For example, the Q factor may be300 or greater.

As described above, according to some implementations, coupling powerbetween two couplers that are in the near-field of one another isdisclosed. As described above, the near-field may correspond to a regionaround the coupler in which mainly reactive electromagnetic fieldsexist. If the physical size of the coupler is much smaller than thewavelength, inversely proportional to the frequency, there is nosubstantial loss of power due to waves propagating or radiating awayfrom the coupler. Near-field coupling-mode regions may correspond to avolume that is near the physical volume of the coupler, typically withina small fraction of the wavelength. According to some implementations,magnetic couplers, such as single and multi-turn conductor loops, arepreferably used for both transmitting and receiving since handlingmagnetic fields in practice is easier than electric fields because thereis less interaction with foreign objects, e.g., dielectric objects andthe human body. Nevertheless, “electric” couplers (e.g., dipoles andmonopoles) or a combination of magnetic and electric couplers may beused.

FIG. 3 is a functional block diagram showing exemplary components ofwireless power transfer system 300, which may be employed in wirelesspower transfer system 100 of FIG. 1 and/or that wireless power transfersystem 200 of FIG. 2 may be part of. The wireless power transfer system300 illustrates a communication link 376, a positioning link 366, using,for example, a magnetic field signal for determining a position ordirection, and an alignment mechanism 356 capable of mechanically movingone or both of the base coupler 304 and the electric vehicle coupler316. Mechanical (kinematic) alignment of the base coupler 304 and theelectric vehicle coupler 316 may be controlled by the base alignmentsubsystem 352 and the electric vehicle charging alignment subsystem 354,respectively. The positioning link 366 may be capable of bi-directionalsignaling, meaning that positioning signals may be emitted by the basepositioning subsystem or the electric vehicle positioning subsystem orby both. As described above with reference to FIG. 1, when energy flowstowards the electric vehicle 112, in FIG. 3 a base charging system powerinterface 348 may be configured to provide power to a base powerconverter 336 from a power source, such as an AC or DC power supply (notshown). The base power converter 336 may receive AC or DC power via thebase charging system power interface 348 to drive the base coupler 304at a frequency near or at the resonant frequency of the base resonantcircuit 206 with reference to FIG. 2. The electric vehicle coupler 316,when in the near-field coupling-mode region, may receive energy from theelectromagnetic field to oscillate at or near the resonant frequency ofthe electric vehicle resonant circuit 222 with reference to FIG. 2. Theelectric vehicle power converter 338 converts the oscillating signalfrom the electric vehicle coupler 316 to a power signal suitable forcharging a battery via the electric vehicle power interface.

The base wireless charging system 302 includes a base controller 342 andthe electric vehicle wireless charging system 314 includes an electricvehicle controller 344. The base controller 342 may provide a basecharging system communication interface to other systems (not shown)such as, for example, a computer, a base common communication (BCC), acommunications entity of the power distribution center, or acommunications entity of a smart power grid. The electric vehiclecontroller 344 may provide an electric vehicle communication interfaceto other systems (not shown) such as, for example, an on-board computeron the vehicle, a battery management system, other systems within thevehicles, and remote systems.

The base communication subsystem 372 and electric vehicle communicationsubsystem 374 may include subsystems or modules for specific applicationwith separate communication channels and also for wirelesslycommunicating with other communications entities not shown in thediagram of FIG. 3. These communications channels may be separatephysical channels or separate logical channels. As non-limitingexamples, a base alignment subsystem 352 may communicate with anelectric vehicle alignment subsystem 354 through communication link 376to provide a feedback mechanism for more closely aligning the basecoupler 304 and the electric vehicle coupler 316, for example viaautonomous mechanical (kinematic) alignment, by either the electricvehicle alignment subsystem 354 or the base alignment subsystem 352, orby both, or with operator assistance.

The electric vehicle wireless charging system 314 may further include anelectric vehicle positioning subsystem 364 connected to a magnetic fieldgenerator 368. The electric vehicle positioning subsystem 364 may beconfigured to drive the magnetic field generator 368 with currents thatgenerate an alternating magnetic field. The base wireless chargingsystem 302 may include a magnetic field sensor 366 connected to a basepositioning subsystem 362. The magnetic field sensor 366 may beconfigured to generate a plurality of voltage signals under influence ofthe alternating magnetic field generated by the magnetic field generator368. The base positioning subsystem 362 may be configured to receivethese voltage signals and output a signal indicative of a positionestimate and an angle estimate between the magnetic field sensor 366 andthe magnetic field sensor 368. These position and angle estimates may betranslated into visual and/or acoustic guidance and alignmentinformation that a driver of the electric vehicle may use to reliablypark the vehicle. In some implementations, these position and angleestimates may be used to park a vehicle automatically with no or onlyminimal driver intervention (drive by wire).

Further, electric vehicle controller 344 may be configured tocommunicate with electric vehicle onboard systems. For example, electricvehicle controller 344 may provide, via the electric vehiclecommunication interface, position data, e.g., for a brake systemconfigured to perform a semi-automatic parking operation, or for asteering servo system configured to assist with a largely automatedparking (“park by wire”) that may provide more convenience and/or higherparking accuracy as may be needed in certain applications to providesufficient alignment between base and electric vehicle couplers 304 and316. Moreover, electric vehicle controller 344 may be configured tocommunicate with visual output devices (e.g., a dashboard display),acoustic/audio output devices (e.g., buzzer, speakers), mechanical inputdevices (e.g., keyboard, touch screen, and pointing devices such asjoystick, trackball, etc.), and audio input devices (e.g., microphonewith electronic voice recognition).

The wireless power transfer system 300 may also support plug-in chargingvia a wired connection, for example, by providing a wired charge port(not shown) at the electric vehicle wireless charging system 314. Theelectric vehicle wireless charging system 314 may integrate the outputsof the two different chargers prior to transferring power to or from theelectric vehicle. Switching circuits may provide the functionality asneeded to support both wireless charging and charging via a wired chargeport.

To communicate between the base wireless charging system 302 and theelectric vehicle wireless charging system 314, the wireless powertransfer system 300 may use in-band signaling via base and electricvehicle couplers 304, 316 and/or out-of-band signaling viacommunications systems (372, 374), e.g., via an RF data modem (e.g.,Ethernet over radio in an unlicensed band). The out-of-bandcommunication may provide sufficient bandwidth for the allocation ofvalue-add services to the vehicle user/owner. A low depth amplitude orphase modulation of the wireless power carrier may serve as an in-bandsignaling system with minimal interference.

Some communications (e.g., in-band signaling) may be performed via thewireless power link without using specific communications antennas. Forexample, the base and electric vehicle couplers 304 and 316 may also beconfigured to act as wireless communication antennas. Thus, someimplementations of the base wireless charging system 302 may include acontroller (not shown) for enabling keying type protocol on the wirelesspower path. By keying the transmit power level (amplitude shift keying)at predefined intervals with a predefined protocol, the receiver maydetect a serial communication from the transmitter. The base powerconverter 336 may include a load sensing circuit (not shown) fordetecting the presence or absence of active electric vehicle powerreceivers in the near-field coupling mode region of the base coupler304.

By way of example, a load sensing circuit monitors the current flowingto a power amplifier of the base power converter 336, which is affectedby the presence or absence of active power receivers in the near-fieldcoupling mode region of the base coupler 304. Detection of changes tothe loading on the power amplifier may be monitored by the basecontroller 342 for use in determining whether to enable the basewireless charging system 302 for transmitting energy, to communicatewith a receiver, or a combination thereof.

As discussed herein, a foreign object may be positioned between awireless power transmitter (e.g., a base pad, base wireless chargingsystem 102, 202, 302, etc., or some other wireless power transfer deviceincluding a coupler (e.g., base coupler 104, 204, 304, etc.)) configuredto emit a wireless power field to a wireless power receiver (e.g., avehicle pad, an electric vehicle wireless charging unit 114, 214, 314,etc., or some other wireless power receiving device including a coupler(e.g., vehicle coupler 116, 216, 316, etc.)). Such foreign objects mayheat up when exposed to a wireless charging field, and may potentiallydamage the wireless power transmitter.

Accordingly, a method and apparatus for protecting a wireless powertransfer pad of a wireless power transmitter as described is desirable.In particular, certain aspects herein provide an at least partially heatsensitive enclosure for a wireless power transfer pad of a wirelesspower transmitter to detect foreign objects. Further, certain aspectscombine heat sensing at a wireless power transfer pad with inductivesensing to detect foreign objects. Though certain aspects and materialsare described herein with respect to materials that change resistancedue to changes in temperature, it should be noted that materials thatchange other types of electrical and non-electrical properties (e.g.,impedance, capacitance, refractive index, mass density, etc.) maysimilarly be used in different aspects and those properties measuredinstead of resistance as described. Detection of changes to theproperties of a heat sensitive material and/or changes to electricalcharacteristics of inductive sense coils may be monitored or measured bya controller such as the base controller 342, or another appropriatecircuit, processor, integrated circuit, etc., which is furtherconfigured to control appropriate action if the detected changes to theproperties of the heat sensitive materials and/or changes to electricalcharacteristics of inductive sense coils indicate presence of a foreignobject. Further, though certain aspects are described herein withrespect to detecting foreign objects at a wireless power transfer pad,similar techniques may be used for foreign object detection for otherimplementations.

In certain aspects, a wireless power transfer pad may include one ormore portions of a heat sensitive enclosure that are aligned with awireless charging field emitted by the wireless power transmitter, suchas a coupler, resonant circuit, etc. The heat sensitive enclosure canadvantageously be configured to or for part of a system configured todetect foreign objects in proximity to the wireless power transfer padas discussed herein. Once the presence of a foreign object is detected,the wireless power transfer system may go into a low power mode, reducepower, turn off, or issue alerts prompting a user to remove the foreignobject. In some aspects, the heat sensitive enclosure may include heatsensitive resistance material and, in some other aspects, the heatsensitive enclosure may include heat sensitive impedance or capacitancematerial. A heat sensitive resistance material may be configured tochange resistance based on a temperature of the material. Similarly, aheat sensitive impedance material, heat sensitive capacitance material,or other heat sensitive material may be configured to change impedance,capacitance, or another electrical or non-electrical property,respectively, based on a temperature of the material.

In some other aspects, the heat sensitive material may constitute awaveguide with one or more wave propagation characteristics beingtemperature sensitive. In some implementations, the heat sensitivematerial constitutes a waveguide for electromagnetic waves e.g. in thevisible light, infrared, or microwave spectrum. In otherimplementations, the heat sensitive material constitutes a waveguide foracoustic waves e.g. ultrasound waves.

Heat sensitive materials for an optical waveguide may include anamorphous quartz glass (e.g. silica or a doped silica), or anothermaterial that is transparent or semi-transparent for electromagneticwaves in the visible light and that exhibit a measurable temperaturesensitive characteristic. Heat sensitive materials of an opticalwaveguide may include materials that produce scattering of lightaccompanied by a spectral shift (wavelength shift) such as Ramanscattering, Rayleigh scattering, or Brillouin scattering. They may alsoinclude materials that change a refracting index (grating) as a functionof temperature.

Heat sensitive materials for a microwave waveguide may include adielectric material with a characteristic (e.g. dielectric constant,loss coefficient, wave impedance, phase velocity, group velocity) thatis heat sensitive.

Heat sensitive materials for an acoustic waveguide may include amaterial with a mass density substantially different from the materialsused of the cover shell and with a wave propagation characteristic (e.g.phase velocity, group velocity, acoustic wave impedance) that is heatsensitive.

In some aspects, traditional materials that may be not be heat sensitivefor protecting an enclosure may include one or more of polyethylene(PE), acrylonitrile butadiene styrene (ABS), polyoxymethylene (POM), andfibre-reinforced epoxy material.

FIG. 4A illustrates an example of an enclosure 400A for a wireless powertransfer pad, in accordance with an illustrative aspect. For example,the wireless power transfer pad may be placed or positioned in theenclosure 400A. In particular, the enclosure 400A includes a cover shell405A and a back plate 410A. In certain aspects, as shown, the covershell 405A is placed over the portion of the wireless power transfer padthat faces a wireless power receiver when wirelessly transferring power.For example, the cover shell 405A may be positioned on a portion of thewireless power transfer pad that faces away from the ground (e.g., thatis up from the ground) when the wireless power transfer pad is placed onthe ground.

In certain aspects, as shown, the back plate 410A is placed below theportion of the wireless power transfer pad that faces a wireless powerreceiver when wirelessly transferring power. For example, the back plate410A may be positioned on a portion of the wireless power transfer padthat faces toward the ground (e.g., that is on the ground) when thewireless power transfer pad is placed on the ground. In certain aspects,the back plate 410A may be omitted and the cover shell 405A may bepositioned over the wireless power transfer pad (e.g., where thewireless power transfer pad is embedded in the ground).

In certain aspects, the back plate 410A is metallic (e.g., aluminum),made of plastic, or may be the same material as the cover shell 405A. Asshown, the entire cover shell 405A may be made of a heat sensitiveresistance (e.g., thermo-resistive) material used to detect the presenceof foreign objects between the wireless power transmitter and thewireless power receiver, as described above, and thus protect thewireless power transfer pad. In some aspects, a heat sensitiveresistance material may be a material that changes its electricalconductivity (e.g., resistance) as a function of temperature. In someaspects, heat sensitive resistance material may have a resistance with ahigh temperature coefficient (e.g., a pronounced NTC (i.e., negativetemperature coefficient) characteristic) such that its resistancesubstantially decreases as temperature rises, and increases astemperature decreases. For example, the conductivity of the heatsensitive resistance material may increase as the temperature passes athreshold. In some aspects, the threshold temperature may be 100° C.

In some aspects, the heat sensitive resistance material may actsubstantially as an insulator at temperatures below a threshold (e.g.,100° C.) and become electrically conductive when the temperature exceedsthe threshold. In some aspects, the heat sensitive resistance materialmay be a doped polymer (e.g. CoolPoly from Celanese) that isnon-conductive or slightly conductive at temperatures of, for example,below 100° C. and whose conductivity increases substantially when thetemperature rises above 100° C.

Further, in some aspects, the heat sensitive resistance material maycombine properties such as pronounced thermo-resistivity with mechanicalstrength, elasticity, heat resistance, and/or thermal conductivity. Insuch aspects, the heat sensitive resistance material may be resistant tomechanical impact, heat, bending, and/or compressive stress. Suchmechanical strength or resistance may protect the wireless powertransfer pad from physical damage. In addition, in such aspects, theheat sensitive resistance material may have an elasticity so as not tobe brittle, thereby allowing the material to sag or bend under pressurewithout breaking (e.g., from a vehicle driving over the cover shell405A). The thermal conductivity, in some aspects, may also preventforeign objects to get excessively hot because a thermal conductivematerial absorbs and dissipates the heat from a hot foreign object awayfrom the back plate 410A. Further, in some aspects, the heat sensitiveresistance material may be suitable for injection molding. In somefurther aspects, the heat sensitive resistance material provides goodmachinability.

In some aspects, the heat sensitive resistance material may be a type ofceramic. In some other aspects, the heat sensitive resistance materialmay be a crystalline material with pronounced NTC characteristics (e.g.due to a phase change in the crystalline structure when temperaturerises). A heat sensitive resistance material with an NTC characteristicdecreases its resistance with an increase in its temperature. Further,in some aspects, the heat sensitive resistance material may be a heatsensitive electrical insulator that becomes conductive at a definedthreshold temperature and remains conductive after the temperature hasdropped below that threshold. In some aspects, the heat sensitiveresistance material may be an electrical conductor with a pronouncedpositive temperature coefficient (PTC). A heat sensitive resistancematerial with a PTC characteristic increases its resistance with anincrease in its temperature (e.g., above a threshold temperature) anddecreases its resistance with a decrease in its temperature (e.g., belowa threshold temperature). Though certain aspects and materials aredescribed herein with respect to materials that change resistance due tochanges in temperature, it should be noted that materials that changeother types of electrical properties (e.g., impedance, capacitance,etc.) may similarly be used in different aspects and those electricalproperties measured. As described above, in some aspects, heat sensitiveimpedance or capacitance material, or other heat sensitive material, maybe used in any of the enclosures described herein in relation to FIGS.4A-4D.

Cover shell 405A, made of the heat sensitive resistance materialdescribed above, may have a size and shape to cover at least the exposedportion of the wireless power transfer pad that is exposed to thewireless power field. As would be understood, cover shell 405A and/orback plate 410A may have any suitable size and/or shape.

FIG. 4B illustrates an example of an enclosure 400B for a wireless powertransfer pad, in accordance with an illustrative aspect. The enclosure400B is similar to enclosure 400A, except that cover shell 405B is notentirely formed of the heat sensitive resistance material. Instead, asshown, cover shell 405B includes a heat sensitive resistance inlay 412Bat the surface of the cover shell 405B. The heat sensitive resistanceinlay 412B may be made of a heat sensitive resistance material asdiscussed herein. Further, the remaining portion of the cover shell maybe made of a non-heat sensitive resistant material or cheaper material.By reducing the amount of heat sensitive resistance material used forcover shell 405B, the cost of enclosure 400B may be reduced, while stilldetecting foreign objects. In certain aspects, the heat sensitiveresistance inlay 412B may cover a portion of the surface of cover shell405B, or the entire surface.

FIG. 4C illustrates an example of an enclosure 400C for a wireless powertransfer pad, in accordance with an illustrative aspect. The enclosure400C is similar to enclosure 400B, in that it includes a heat sensitiveresistance inlay 412C, except that the heat sensitive resistance inlay412C is embedded in the cover shell 405C instead of being at the surfaceof the cover shell 405C.

FIG. 4D illustrates an example of an enclosure 400D for a wireless powertransfer pad, in accordance with an illustrative aspect. Enclosure 400Dis similar to enclosures 400B and 400C, in that it includes a heatsensitive resistance inlay 412D (e.g., at the surface, or embedded inthe cover shell 405D), except that cover shell 405D further includesheat resistant inlay 413. In enclosure 400D, heat sensitive resistanceinlay 412D may be embedded in cover shell 405D (e.g. a few millimetersbelow the surface) while heat resistant inlay 413 may be placed above atthe surface of cover shell 405D. In some aspects, heat sensitiveresistance inlay 412D and heat resistant inlay 413 may be adjacent, asshown in FIG. 4D. In some other aspects, the entire cover shell 405D maybe made of the heat sensitive resistant material with the heat resistantinlay 413 embedded in cover shell 405D. In some further aspects, theentire cover shell 405D may be made of a heat resistant material withthe heat sensitive resistance inlay 412D embedded in cover shell 405D.

Heat resistant inlay 413 may include a heat resistant material able towithstand temperatures reached by foreign objects (e.g. over 200° C.,300° C., 400° C., etc.). In some aspects, the heat resistant materialmay have a melting point of, for example, above 200° C. and may have aheat conductivity that is substantially higher than that of prevalentplastic material. In some aspects, the heat resistant material may beflame retardant. In some aspects, the heat resistant material may alsobe resistant to mechanical impact, bending, and/or compressive stress.Such mechanical resistance may protect the wireless power transfer padfrom physical damage. In some aspects, the heat resistant material mayhave an elasticity so as not to be brittle, thereby allowing thematerial to sag or bend under pressure without breaking (e.g., from avehicle driving over the cover shell 405A). In some aspects, the heatresistant material may have a high thermal conductivity to dissipateheat (e.g., heat produced by a foreign object). In some aspects, theheat resistant material is resistant to long term ultraviolet (UV)exposure. In some aspects, the heat resistant material is resistant todamage from chemical substances (e.g., lubricating and diesel oils,gasoline, brake fluid, coolant, solvents, etc.). In some aspects, theheat resistant material has a low thermal expansion to avoid bulging ordeformation due to heat (e.g., from the foreign object). In someaspects, the heat resistant material is electrically non-conductive,such as to not generate eddy or displacement currents when exposed to awireless power field. In some aspects, the heat resistant material isnon-magnetic to avoid interaction with the wireless power field. In someaspects, the heat resistant material is low cost. In some aspects, theheat resistant material has a high autoignition temperature. In someaspects, the heat resistant material provides good machinability.Further, in some aspects, the heat resistant material may be suitablefor injection molding.

For example, the heat resistant material of heat resistant inlay 413 mayinclude one or more of plastics such as nylon resins (e.g., Minlon,Zytel from Dupont, etc.), perfluoroelastomers (e.g., Kalrez fromDupont), polymerized siloxanes (e.g., silicone rubber), glass orcarbon-fibre reinforced plastics, structural composites (e.g., PyroSic,PyroKarb from Pyromeral systems), a sintered high temperature polymer(e.g. polyimides (PI) such as TECASINT from Ensinger), and/or ceramicmatrix composites (CMC) (e.g., glass-ceramics). In some aspects, theheat resistant material may include multiple layers, such as a layerincluding a first plastic material with a high heat resistance (e.g.,greater than 200° C.) and a high ignition temperature (e.g., greaterthan 600° C.), and a second layer including a highly heat resistant meshstructure (e.g., greater than 600° C.) made of a second material, suchas carbon fibers, that prevent an object from sinking into the padenclosure when the first plastic material starts melting. In someaspects, hot foreign objects laying on the wireless power transfer pad'ssurface may be detected by sensing a change in the electrical resistanceof heat sensitive resistance inlay 412D.

FIG. 5 illustrates an example of heat sensitive resistance layer 500, inaccordance with an illustrative aspect. For example, heat sensitiveresistance layer 500 may be made of at least one heat sensitiveresistance material that is configured to change resistance based on atemperature of the material (e.g., as discussed). The heat sensitiveresistance layer may include a cable comprising at least twoelectrically conductive wires 564 embedded in insulation 562, which mayinclude heat sensitive resistance material. The cable may be arranged inserpentines as shown in FIG. 2 or in a spiral or meandering structure tocover the wireless power transfer pad's surface, where foreign objects(e.g. metallic objects) may get hot if exposed to the inductive powertransfer (IPT) magnetic fields. In some aspects, the presence of a hotforeign object 560 laying on the wireless power transfer pad's surfacemay result in a local change of the resistance of cable insulation 562(e.g., the local resistance may decrease). Accordingly, the presence ofthe hot foreign object may be detected by sensing a change in theresistance based on change in resistance of the cable insulation 562. Insome aspects, this may be performed by measuring the resistance betweenterminals a and b as shown in FIG. 5. In such aspects, the cable wiresmay be open circuited throughout the cable. For example, since the cableinsulation 562 is made of a heat sensitive resistance material, theconductivity of the cable insulation 562 changes as the temperature ofthe cable insulation 562 (e.g., based on exposure to the hot foreignobject) changes. Since terminals a and b are open circuited, the onlyelectrical path between terminals a and b is via the cable insulation562. Therefore, a measure of the resistance between terminals a and b isalso a measure of resistance/conductivity of the cable insulation 562.Accordingly, a change in temperature of the cable insulation 562 changesa measure of resistance between terminals a and b. In certain aspects,the terminals a and b are coupled to a controller (e.g., base controller342) or other measuring circuit, which measures theresistance/conductivity between terminals a and b (e.g., of the cableinsulation 562). The measuring circuit may further be coupled to acontroller (e.g., base controller 342) which takes appropriate actionbased on the measured resistance/conductivity. For example, if themeasured resistance/conductivity does not satisfy a threshold forindicating presence of a foreign object, the controller may take noaction/allow wireless power transfer to continue. In another example, ifthe measured resistance/conductivity does satisfy a threshold forindicating presence of a foreign object, the controller may take actionto stop or restrict wireless power transfer and/or generate an alert(e.g., audible, visual, etc.).

FIG. 6 illustrates an example of a circuit corresponding to the cableshown in FIG. 5, in accordance with an illustrative aspect. FIG. 6 showsa series of discrete resistances Rp connected in parallel correspondingto the resistance of the cable insulation (e.g., 562) between theconductive wires a and b (e.g., 564). In some aspects, resistance Rp (asshown by the arrow) may change when in proximity of hot foreign object660. This change in resistance may result in a change of sense currentIs if sense voltage Vs is applied across terminals a and b (e.g., ameasuring circuit). In the parallel arrangement, shown in FIG. 6, achange of resistance Rp may be particularly pronounced if the heatsensitive resistance material in the insulation around the conductivewires has an NTC characteristic. In some aspects, the heat sensitiveresistance insulator (e.g. insulator 562) may produce an electricalshort circuit once the temperature has exceeded a defined threshold,such as 200° C.

FIG. 7 illustrates an example of a heat sensitive resistance layer 700,in accordance with an illustrative aspect. As shown in FIG. 7, heatsensitive resistance layer 700 may include a top conductive wire grid(electrode a) 770, a bottom conductive wire grid (electrode b) 772, andan intermediate layer of heat sensitive resistance material 762. Asdescribed above in relation to FIGS. 5 and 6, the presence of a hotforeign object laying on the wireless power transfer pad's surface maybe detected by sensing a change in the resistance as measured betweenterminals a and b. This is because heat sensitive resistance material762 may become conductive when a certain temperature is exceeded. Thismay then result in a low resistance circuit whereby top conductive wiregrid 770 may conduct to bottom conductive wire grid 772 through heatsensitive resistance material 762. The low resistance as measuredbetween terminals a and b may then indicate the presence of a hotforeign object.

In some aspects, the conductive wire grid (e.g. 770 and 772, combined)may be designed such that reduced eddy current losses occur in thepresence of strong IPT magnetic fields (avoiding current loops). In someaspects, other electrode grid structures may apply as well (e.g.serpentine or meander-shaped structures). In some aspects, heatsensitive resistance layer 762 may be a printed wire board (PWB) withthin conductive traces minimizing eddy current losses. In some aspects,this PWB may also integrate the sense coils of an inductivesensing-based foreign object detection system.

FIG. 8 illustrates an example of a heat sensitive resistance layer 800,in accordance with an illustrative aspect. Heat sensitive resistancelayer 800 is similar to heat sensitive resistance layer 700, except thatin FIG. 8 conductive wire grids 870 a and 870 b (electrodes a and b) aredisposed only on one side of heat sensitive resistance layer 800. Insome aspects, as shown in FIG. 8, the conductive wire grids 870 a and870 b may be placed on top of heat sensitive resistance material 862. Insome aspects, conductive wire grids 870 a and 870 b may be interleavedas shown in FIG. 8. In some aspects (not shown), interleaved serpentine,spiral or meander-shaped electrode structures may be disposed on oneside of heat sensitive resistance layer 800. Sensing a change inresistance, detecting a foreign object, and/or protecting the wirelesstransfer pad by shorting the circuit may all be performed as describedin relation to FIGS. 5-7.

In some aspects, sensing a change of a resistance may also be performedon a more spatially selective basis using an array (matrix) ofresistance cells connected to a switch matrix (multiplexer). FIGS. 9Aand 9B illustrate exemplary aspects of a selective heat sensitiveresistance array, in accordance with an illustrative aspect. FIG. 9B isa more detailed view of a heat sensitive resistance cell including aheat sensitive resistance material as previously described. As shown inFIG. 9A, a hot foreign object may be detected by sensing an electricalresistance between terminals a and b and by closing one switch pair at atime (e.g., according to a time multiplexing scheme) (e.g., ascontrolled by a controller, such as base controller 342). For instance,when the two switches corresponding to a cell are closed, resistance ofthe individual cell may be measured, such as described with respect toFIG. 5.

In some aspects (not shown), the array may comprise a small number ofheat sensitive resistance cells (e.g. only 4×4), each cell covering asignificant portion of the area to be monitored. In such aspects, eachcell may be contacted by an electrode grid as illustrated in FIG. 7.Dividing the area of the heat sensitive resistance layer in portions mayenhance the hot foreign object detection system in terms of sensitivityand reliability.

In certain aspects, a selective heat sensitive resistance array, mayfurther be used to determine a location of a foreign object within anarea of the heat sensitive resistance array. For example, as described,resistance of individual cells may be measured. Accordingly, if theresistance of a particular cell indicates presence of a foreign object,then the controller determines the foreign object is in the area wherethe particular cell is located. For example, the controller may haveinformation about a position of each cell in the heat sensitive arrayand determine a position of the foreign object based on the position ofthe cell indicating presence of the foreign object.

In some further implementations (not shown), the heat sensitiveresistance layer may be a single plate 762 as illustrated in FIG. 7, butwith its connecting electrodes switched with a switched matrix as shownin FIG. 9A. This may be considered as a combination of theimplementation of FIG. 7 with the implementation of FIG. 9A.

In some embodiments of heat sensitive resistance layer 500 of FIG. 5(e.g., the cable shown), a suitable heat sensitive resistance materialmay be used for the conductive wires (e.g. 564) or, in some aspects, forone or both of conductive wires and the insulation (e.g. 562) of FIG. 5.In such aspects, conductive wires 564 may be preferably made of materialwith a PTC characteristic. A corresponding lumped element circuit modelcomprising a series of resistances Rs, connected in series, isillustrated in FIG. 10. In such aspects, a hot foreign object inproximity of one of resistances Rs may increase the resistance ofconductive wires 564. In such aspects, the wire resistance may bemeasured at terminals a and b with a short circuit at the other end ofthe cable, as shown in FIG. 10. To minimize eddy current losses andinterference of the resistance measurement, the separation between theat least two conductive wires of the heat sensitive resistance cable maybe minimal and/or the conductive wires may be twisted.

In some embodiments of heat sensitive resistance layer 500 of FIG. 5,the material used for the conductive wires (e.g. 564) may be a materialthat becomes substantially non-conductive when a temperature exceeds adefined threshold so that a high resistance (e.g., substantially open)is measured between terminals a and b, provided that the wire ends areshort circuited (not shown in FIG. 5).

In some aspects, a heat sensitive impedance material may be used in allthe embodiments described in relation to FIGS. 4 through 10. Heatsensitive impedance material may be material that changes its impedance(e.g., resistance and/or capacitance, inductance) as temperature rises.In such aspects, the change in impedance may be sensed using an AC or apulsed signal source in the measuring circuit.

In some implementations using an electromagnetic or acoustic waveguidewith one or more temperature sensitive characteristics as previouslydescribed, the waveguide may be an optical fiber, a tube filled with adielectric material or a gas. The heat sensitive waveguide may bedisposed in a manner as previously described in connection with FIG. 5,e.g. in form of serpentines, meanders, spirals, etc. in a layer belowthe surface of the wireless power transfer pad. In some otherimplementations, the heat sensitive waveguide may have the shape of aplate (layer) 762 as previously described in connection with FIG. 7.

In some aspects, hot foreign object detection using a heat sensitiveresistance layer, as described above, may be combined with additionaldiscrete temperature sensors that may be integrated into the wirelesspower transfer pad. In some aspects, such sensors may provide indicationof a general increase of the wireless power transfer pad's temperature(e.g. during active power transfer) and, therefore, improve reliabilityof hot foreign object detection. Such sensors may be coupled with acontroller (e.g., controller 342) configured to control wireless powertransfer of the wireless power transfer pad. For example, in certainaspects, if both the temperature sensors sense a temperature above afirst threshold indicative of presence of a foreign object, and themeasured characteristic of the heat sensitive material satisfies athreshold indicative of presence of a foreign object, the controllerdetermines a foreign object is present and takes appropriate action. Incertain aspects, if either the temperature sensors do not sense atemperature above the first threshold, or the measured characteristic ofthe heat sensitive material does not satisfy the threshold indicative ofpresence of a foreign object, the controller determines a foreign objectis not present and takes appropriate action. In certain aspects, ifeither the temperature sensors sense a temperature above the firstthreshold, or the measured characteristic of the heat sensitive materialdoes satisfy the threshold indicative of presence of a foreign object,the controller determines a foreign object is present and takesappropriate action. In certain aspects, if the temperature sensors sensea temperature above the first threshold, the controller only thenmeasures the characteristic of the heat sensitive material and takesappropriate action based on whether the measured characteristic does ordoes not satisfy the threshold indicative of presence of a foreignobject. In certain aspects, if the measured characteristic of the heatsensitive material does satisfy the threshold indicative of presence ofa foreign object, only then the controller uses the temperature sensorsto sense the temperature, and based on whether the sensed temperature isabove or below the first threshold, takes appropriate action.

In some aspects, sensing a heat sensitive characteristics of a materialmay also allow determining a spatial profile or a spatial distributionof this heat sensitive characteristics over the area covered by theforeign object detection system using the controller. In someimplementations, such a distribution is determined using a plurality ofheat sensitive resistance cells as shown in FIG. 9A. In some otherimplementations, some spatial resolution of a heat sensitivecharacteristics may be provided using a cable with a heat sensitiveresistance as previously described in connection with FIG. 5 e.g. byemploying a time domain or frequency domain reflectometry method. Insome further implementations based on acoustic or electromagneticwaveguides e.g. an optical fiber as previously described, a spatialprofile is determined e.g. using a time domain or frequency domainreflectometry method.

In a further aspect, spatial resolution may be used for determiningpresence of a hot foreign object based on a space-differential detectionapproach. In some implementations employing a space-differential scheme,decision on presence of a hot object may be made based upon a ratio of apeak value to an average value of a sensed characteristic of atemperature sensitive material by the controller. For example, if theratio satisfies a threshold (e.g., is above a threshold) the controllerdetermines a foreign object is present and takes appropriate action. Ifthe ratio does not satisfy the threshold, the controller determines aforeign object is not present and takes appropriate action. In someother implementations, a decision is made based upon a ratio of a peakvalue to a median value or another percentile of a discretizeddistribution of a sensed heat sensitive characteristic of a material.For example, in certain aspects the ambient temperature or temperaturenear the wireless power transfer pad may be high (e.g., on a hot day).Accordingly, in such aspects, if the ambient temperature is high enoughto cause the sensed characteristic of a temperature sensitive materialto be above a set threshold for detecting a foreign object, then thecontroller may determine a foreign object is present when it is not,leading to a false positive. However, if spatial resolution is used fordetermining presence of the foreign object, then even if the ambienttemperature is high across the wireless power transfer pad (e.g., acrosscells of a heat sensitive array), the cells are less likely to have apeak value such that the ratio of the peak value to the average valueacross the cells is above a threshold unless a foreign object ispresent, thereby reducing the likelihood of a false positive. Further,even if the temperature sensitive material does not provide accuratemeasurements of temperature, it may provide precise measurements suchthat the ratio of peak value to average value does not vary as much fromone implementation to another, thereby making relative measurementseasier to use for control of the wireless power transfer pad.

In yet a further aspect, presence of a hot foreign object may bedetermined based on a time-differential approach and decision is madebased on a level of temporal change (rate of change) of a sensedcharacteristic of a temperature sensitive material, e.g. by employing adifferentiator or high pass filter upon successively sensed values. Forexample, in certain aspects, an object near a wireless power transferpad may be hot, but not correlated to the output of the wireless powertransfer pad. For example, an object near the wireless power transferpad may stay at a steady temperature regardless of whether the wirelesspower transfer pad is transferring power or not. Further, in certainaspects, the ambient temperature near the wireless power transfer padmay be generally high, but not changing. Accordingly, utilizing the rateof change of a sensed characteristic can be used to determine a rate ofchange in temperature. If temperature is not changing by a threshold,than there may not be a foreign object, and rather the generaltemperature near the wireless power transfer pad may be hot. However, ifthe temperature is changing by a threshold, it may indicate the objectwill heat up further, and may be a foreign object. Some implementationsmay employ both space and time-differential detection.

In some aspects, the electrode grid structure used for heat sensitiveresistance sensing, as shown in FIGS. 7 and 8, may also be used forcapacitively sensing objects (e.g. living objects) located near thesurface of a wireless power transfer pad. The various detection methodsmay be employed by a measuring circuit and/or controller, as discussed.

In some aspects, sense coils of an inductive sensing foreign objectdetection system (e.g., inductive foreign object detector) may be usedas additional temperature sensors (e.g., by measuring the impedance, andparticularly the resistance of the sense coils) along with a heatsensitive material based detection. For example, such an inductiveforeign object detector may correspond to the previously describedadditional discrete temperature sensors.

An exemplary inductive foreign object detector is illustrated in FIG.11. The inductive foreign object detector 1100 may use a plurality ofinductive sense coils 1102 operationally connected via series capacitor1104 and multiplexer 1108 to a detection circuit 1110 (e.g., a measuringcircuit, a controller (e.g., base controller 342), etc.). Though only asingle inductive sense coil 1102 is shown in FIG. 11, in certainaspects, a plurality of inductive sense coils 1102 may be used forinductive foreign object detection. Though illustrated as a “circular”coil, sense coils 1102 may be “double-D” coils or other conductive wirestructures. The plurality of sense coils 1102 may be an array ofsubstantially coplanar coils arranged in rows and columns (not shown).In certain aspects, the plurality of sense coils 1102 are disposed ontop of a wireless power transfer pad. In certain aspects, the pluralityof sense coils 1102 may be positioned similar to a heat sensitivematerial such as described with respect to FIGS. 4A-4D. In certainaspects, the plurality of sense coils 1102 may be included along withthe heat sensitive material and either in the same position (e.g.,substantially same plane) or different position (e.g., above or below)as the heat sensitive material. For example, in certain aspects, theplurality of sense coils 1102 are positioned (e.g., closely) below theupper surface (e.g., cover shell, such as any of cover shell 405A-405D)of an enclosure (e.g., any of enclosure 400A-400D) facing towards awireless power receiver. In certain aspects, the detection circuit 1110is configured to measure an electrical characteristic of each of theplurality of sense coils 1102 in a time-multiplexed fashion. Thecharacteristic may include at least one of an impedance, a resistance,an induced voltage, or an impulse response. In certain aspects, thedetection circuit 1110 applies a sense current having a frequency to then-th sense coil 1102 as selected by the multiplexer 1108 e.g. formeasuring an impedance Z_(s,n) at the measuring port as indicated inFIG. 11 by Z_(s). A change in the impedance Z_(s,n) relative to areference value (e.g., by a threshold) may indicate presence of aforeign object 1160. In certain aspects, the sense frequency isconsiderably above the frequency used for wireless power transfer (e.g.,operating frequency of base coupler 204), e.g. in the MHz range. Seriescapacitor 1104 and shunt inductor 1106 may act as a high pass filterattenuating the voltage induced into the sense coil 1102 by a strong lowfrequency electromagnetic field (<150 kHz) used for wireless powertransfer. In some implementations, series capacitor 1104 and theinductance of the sense coil 1102 are configured to form a resonance atthe sense frequency. Measuring the impedance at or near resonance may beadvantageous in some implementations.

In further aspects, inductive foreign object detection is based onmeasuring a voltage induced into a sense coil 1102 by the magnetic fieldas generated by another coil different from the sense coil (e.g. thecoil of the base coupler 304 with reference to FIG. 3). In someimplementations, the magnetic field is the magnetic field as used forwireless power transfer, and capacitor 1104 and shunt inductor 1106 areomitted and there is virtually no current flowing in the sense coil 1102for the purpose of inductive sensing.

In some aspects, the circuit illustrated in FIG. 11 may combineinductive sensing and heat sensing by using sense coils that are made ofa heat sensitive conductor material 1164 (e.g., a heat sensitivematerial as discussed herein, such as with respect to wires 564 andinsulation 562) that changes its resistance (e.g. or other electricalcharacteristic as described) (e.g., substantially) when temperatureexceeds a threshold (e.g., critical level). In certain aspects, aforeign object 1160 which may not be detected by inductive sensing(e.g., too small in size and/or due to positioning or orientation withrespect to the sense coil 1102) may be detected by its thermal effect,e.g., by sensing a change in a resistance of the heat sensitiveconductor material 1164 of heat sensitive sense coil 1102.

In further aspects, one or more of the plurality of sense coils 1102 maybe bifilar (e.g., including two separate wires (e.g., approximately inparallel and closely spaced)) winding structures as illustrated in FIGS.12A to 12C for example. For example, in certain aspects, sense coil 1102comprises separate windings that are electrically insulated from eachother using a heat sensitive material (e.g., heat sensitive resistancematerial) that changes its insulation resistance based on temperature(e.g., locally in presence of a hot object 1160 laying on the surface ofa wireless power transfer pad as previously described in connection withFIG. 5). For example, the windings may comprise conductive wires 564 asshown. Further, in certain aspects, the heat sensitive materialinsulating conductive wires 564 from each other comprises heat sensitiveinsulation 562 (e.g., a cable insulation 562 around the conductive wires564 as illustrated in FIG. 12A). Alternatively, the bifilar wirestructure comprising conductive wires 564 may be embedded in a heatsensitive resistance layer 1262 e.g. as previously described inconnection with FIGS. 4A to 4D. In some implementations (not shown), thebifilar winding structure (e.g., conductive wires 564) may be a twistedpair. In some implementations, a first sense coil winding (e.g., firstconductive wire 564) and a second sense coil winding (e.g., secondconductive wire 564) are disposed in the same plane e.g. embedded in aheat sensitive resistance layer 1262 as illustrated in FIG. 12B. Infurther implementations, a first sense coil winding (e.g., firstconductive wire 564) and a second sense coil winding (e.g., secondconductive wire 564) are disposed in different planes and the heatsensitive resistance layer 1262 is between the two planes. Asillustrated in FIG. 12C, a first sense coil winding (non-dashed line)(e.g., first conductive wire 564) may contact a top surface of a heatsensitive resistance layer 1262 while a second sense coil winding (e.g.,second conductive wire 564) (dashed-line) may contact a bottom surfaceof the heat sensitive resistance layer 1262. In yet a further aspect, atleast one of the conductive wires 564 of the bifilar sense coil 1102 ismade of a heat sensitive material that changes its resistance (oranother electrical characteristic) (e.g., substantially) when atemperature of the heat sensitive material exceeds a threshold (e.g.,critical level), e.g., as previously described in connection with FIG.10.

In some aspects, FIG. 13A illustrates an exemplary combined inductiveand heat sensing foreign object detector 1300 using a plurality ofbifilar sense coils 1102 (e.g., as described with respect to any ofFIGS. 12A to 12C) in accordance with certain aspects. Terminals 1 a and1 b of a first sense coil winding comprising a conductive wire 564 ofsense coil 1102 may be operationally connected via series capacitor 1104and a first multiplexer 1108 to an impedance measuring port Z_(s) ofdetection circuit 1310 (e.g., a measuring circuit, a controller (e.g.,base controller 342), detection circuit 1110, etc.). Terminals 1 a and 2a of the first sense coil windings and a second sense coil windingcomprising a conductive wire 564 of sense coil 1102, respectively, maybe operationally connected via a second multiplexer 1308 to aninsulation resistance measurement port denoted by R_(oc) of detectioncircuit 1310, while terminal 2 b of the second sense coil winding may beopen circuited. In certain aspects, the first and second sense coilwindings are insulated from each other by a heat sensitive material suchas a heat sensitive insulation 562 (not shown) or a heat sensitiveresistance layer 1262 (as shown). Both measurement ports may have acommon ground as indicated in FIG. 13A. In some implementations, thedetection circuit 1310 is configured to measure the (e.g., DC insulation(e.g., open circuit)) resistance between the first sense coil windingand the second sense coil winding. A change in the open circuitresistance R_(oc) relative to a reference value (e.g., a threshold) maybe indicative of the presence of a foreign object 1160. Capacitor 1304may be configured to serve as low pass filter to reject potentialfrequency components induced by the electromagnetic field used forwireless power transfer and/or by a high frequency sense field from thesense coil 1102 as used for inductive sensing.

In certain aspects, for each sense coil 1102, to perform inductivesensing, the first multiplexer 1108 couples terminals 1 a and 1 b of thefirst sense coil winding to the impedance measuring port Z_(s) ofdetection circuit 1310. The detection circuit 1310 measures impedance atthe impedance measurement port and determines if a foreign object ispresent based on the measured impedance (e.g., as described with respectto FIG. 11).

In certain aspects, for each sense coil 1102, to perform heat sensing,the second multiplexer 1308 couples terminals 1 a and 2 a of the firstsense coil winding and the second sense coil winding to the insulationresistance measurement port denoted by R_(oc) of detection circuit 1310.The detection circuit 1310 measures resistance at the resistancemeasurement port and determines if a foreign object is present based onthe measured resistance (e.g., as described with respect to FIG. 12).

FIG. 13B illustrates another exemplary implementation of a combinedinductive and heat sensing foreign object detector 1302 including aplurality of bifilar sense coils 1102 made of a heat sensitive conductormaterial 1164. In certain aspects, unlike detector 1300, in detector1302, terminals 1 b and 2 b of the first sense coil winding and thesecond sense coil winding, respectively, are short circuited, and atleast one of the first sense coil winding and the second sense coilwinding comprises heat sensitive conductor material 1164. Further, incertain aspects, in detector 1302, detection circuit 1310 is configuredto measure the resistance of the conductive structure (e.g., windingscomprising heat sensitive conductor material 1164) of sense coil 1102.In some aspects, the detection circuit 1310 measures the short circuitDC resistance R_(oc). A change in the short circuit DC resistance R_(oc)relative to a reference value (e.g., a threshold) may be indicative ofthe presence of a foreign object 1160. In certain aspects, heatdetection based on a DC resistance measurement R_(oc) as illustrated inFIG. 13B may be more sensitive and reliable than measuring the impedanceZ_(s) (e.g. at high frequency) as illustrated in FIG. 11.

The implementations as illustrated in FIGS. 11, 12, and 13 should beconstrued as exemplary and non-limiting. They do not represent the onlyimplementations of a combined inductive and heat sensing foreign objectdetector. For example, in certain aspects, a combined inductive and heatsensing foreign object detector may include a separate inductive foreignobject detector (e.g., foreign object detector 1100) and a separate heatsensing foreign object detector (e.g., as described with respect toFIGS. 4-10. In certain aspects, whether separate or integrated (e.g., asdiscussed with respect to FIG. 13), the detection parameters (e.g.,resistance, capacitance, etc.) from the heat sensing detection and thedetection parameters (e.g., impedance, a resistance, an induced voltage,or an impulse response) from the inductive sensing detection may becombined to control wireless power transfer.

For example, each of the heat sensing detection system and the inductivesensing detection system may be coupled to a controller (e.g.,controller 342, detection circuit, etc.) configured to control wirelesspower transfer of a wireless power transfer pad. For example, in certainaspects, if both the inductive sensing detection system senses anelectrical characteristic that satisfies a threshold (e.g., firstthreshold) indicative of presence of a foreign object, and the heatsensing detection system senses an electrical characteristic thatsatisfies a threshold (e.g., second threshold) indicative of presence ofa foreign object, the controller determines a foreign object is presentand takes appropriate action.

In certain aspects, if either the inductive sensing detection systemsenses an electrical characteristic that does not satisfy the thresholdindicative of presence of a foreign object, or the heat sensingdetection system senses an electrical characteristic that does notsatisfy the threshold indicative of presence of a foreign object, thecontroller determines a foreign object is not present and takesappropriate action. In certain aspects, if either the inductive sensingdetection system senses an electrical characteristic that satisfies thethreshold indicative of presence of a foreign object, or the heatsensing detection system senses an electrical characteristic thatsatisfies the threshold indicative of presence of a foreign object, thecontroller determines a foreign object is present and takes appropriateaction. In certain aspects, if the heat sensing detection system sensesan electrical characteristic that satisfies the threshold indicative ofpresence of a foreign object, the controller only then directs theinductive sensing detection system to measure the electricalcharacteristic and takes appropriate action based on whether themeasured electrical characteristic does or does not satisfy thethreshold indicative of presence of a foreign object. In certainaspects, if the inductive sensing detection system senses an electricalcharacteristic that satisfies the threshold indicative of presence of aforeign object, the controller only then directs the heat sensingdetection system to measure the electrical characteristic and takesappropriate action based on whether the measured electricalcharacteristic does or does not satisfy the threshold indicative ofpresence of a foreign object. In certain aspects, the results of one ofthe inductive sensing system and the heat sensing system is used tocontrol the other of the inductive sensing system and the heat sensingsystem.

In some aspects, once the presence of a hot foreign object is detected(as described above in relation to FIGS. 5-13), the wireless chargingsystem may take one or more actions. For instance, the system may gointo a low power mode, reduce power, turn off, or issue alerts promptinga user to remove the object. Further, in some aspects, the detection ofa hot foreign object may be made more reliable by correlating the sensedchange of a characteristics of a temperature sensitive material orinductive sensing, as described above in relation to FIGS. 5-13, with alevel of the alternating magnetic field as generated by the wirelesspower transfer pad. The generated alternating magnetic field may relateto the transfer of power between the wireless power transfer device andthe wireless power receiver. For instance, a change in an electricalcharacteristic (e.g., resistance) when power is being transmitted, mayillustrate a higher chance of the change in resistance being due to thepresence of a hot foreign object and vice versa.

In some other aspects, the detection of a hot foreign object may be mademore reliable by correlating the sensed change of a characteristics of atemperature sensitive material or inductive sensing, as described abovein relation to FIGS. 5-13, with an output of another foreign objectdetector e.g., based on microwave radar sensing, infrared sensing e.g.using a vehicle underbody mounted camera, etc.

FIG. 14 illustrates example operations for performing combined inductivesensing and heat sensing for foreign object detection, in accordancewith an illustrative aspect. In certain aspects, the operations 1400 maybe performed by a controller.

Operations 1400 begin at optional 1402 where power is wirelesslytransferred at a wireless power transfer pad. At 1404, a change in aproperty of a heat sensitive material positioned near the wireless powertransfer pad is determined. At 1406, a change in an electricalcharacteristic of one or more sense coils is determined, wherein the oneor more sense coils are positioned near the wireless power transfer pad.At 1408, presence of a foreign object is detected (and optionallywirelessly transferring the power is adjusted or an alert is generated)based on at least one of the determined change in the property of theheat sensitive material or the determined change in the electricalcharacteristic of one or more sense coils.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication-specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database, or another data structure), ascertaining, and thelike. Also, “determining” may include receiving (e.g., receivinginformation), accessing (e.g., accessing data in a memory), and thelike. Also, “determining” may include resolving, selecting, choosing,establishing, and the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an ASIC, a field programmable gate array (FPGA) or otherprogrammable logic device (PLD), discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but in the alternative, the processor may be anycommercially available processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in hardware, anexample hardware configuration may comprise a processing system in awireless node. The processing system may be implemented with a busarchitecture. The bus may include any number of interconnecting busesand bridges depending on the specific application of the processingsystem and the overall design constraints. The bus may link togethervarious circuits including a processor, machine-readable media, and abus interface. The bus interface may be used to connect a networkadapter, among other things, to the processing system via the bus. Thenetwork adapter may be used to implement the signal processing functionsof the physical (PHY) layer. In the case of a user terminal, a userinterface (e.g., keypad, display, mouse, joystick, etc.) may also beconnected to the bus. The bus may also link various other circuits suchas timing sources, peripherals, voltage regulators, power managementcircuits, and the like, which are well known in the art, and therefore,will not be described any further.

The processing system may be configured as a general-purpose processingsystem with one or more microprocessors providing the processorfunctionality and external memory providing at least a portion of themachine-readable media, all linked together with other supportingcircuitry through an external bus architecture. Alternatively, theprocessing system may be implemented with an ASIC with the processor,the bus interface, the user interface in the case of an accessterminal), supporting circuitry, and at least a portion of themachine-readable media integrated into a single chip, or with one ormore FPGAs, PLDs, controllers, state machines, gated logic, discretehardware components, or any other suitable circuitry, or any combinationof circuits that can perform the various functionality describedthroughout this disclosure. Those skilled in the art will recognize howbest to implement the described functionality for the processing systemdepending on the particular application and the overall designconstraints imposed on the overall system.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A foreign object detection system comprising: aheat sensing system comprising: an insulation layer including a heatsensitive material having a property configured to change as a functionof temperature; and at least two electrically conductive wires; aninductive sensing system comprising one or more sense coils and at leastone of the at least two electrically conductive wires, wherein a changein an electrical characteristic of the one or more sense coils isindicative of a presence of a foreign object; and a controller coupledto the heat sensing system and the inductive sensing system, thecontroller being configured to determine the presence of the foreignobject based on at least one of a measure of the property of the heatsensitive material or a measure of the electrical characteristic of theone or more sense coils.
 2. The foreign object detection system of claim1, wherein the at least two electrically conductive wires are at leastone of embedded in the insulation layer, on a same plane and in contactwith the insulation layer, or on separate planes in contact withseparate surfaces of the insulation layer.
 3. The foreign objectdetection system of claim 1, wherein the property comprises anelectrical conductivity, and wherein the controller is configured todetermine the presence of the foreign object based on the change in theelectrical conductivity satisfying a threshold.
 4. The foreign objectdetection system of claim 1, wherein the heat sensing system comprises aplurality of heat sensitive cells.
 5. The foreign object detectionsystem of claim 1, wherein the controller is configured to determinethat the foreign object is present when either the measure of theproperty of the heat sensitive material or the measure of the electricalcharacteristic of the one or more sense coils indicate the presence ofthe foreign object.
 6. The foreign object detection system of claim 1,wherein the controller is configured to control the inductive sensingsystem based on the measure of the property of the heat sensitivematerial.
 7. The foreign object detection system of claim 1, wherein thecontroller is configured to control the heat sensing system based on themeasure of the electrical characteristic of the one or more sense coils.8. The foreign object detection system of claim 1, wherein the heatsensing system and the inductive sensing system share one or morecomponents.
 9. The foreign object detection system of claim 8, whereinthe one or more sense coils comprise the heat sensitive material. 10.The foreign object detection system of claim 1, wherein the heat sensingsystem comprises a first electrically conductive wire and a secondelectrically conductive wire, wherein a first sense coil of theinductive sensing system comprises the first electrically conductivewire, wherein a first terminal of the first electrically conductive wireand a second terminal of the first electrically conductive wire areselectively coupled to an impedance measuring port of the controller,and wherein the first terminal of the first electrically conductive wireand a first terminal of the second electrically conductive wire areselectively coupled to a resistance measurement port of the controller,wherein the controller is configured to measure the property of the heatsensitive material by measuring resistance at the resistance measurementport, and wherein the controller is configured to measure the electricalcharacteristic of the first sense coil by measuring impedance at theimpedance measuring port.
 11. The foreign object detection system ofclaim 10, wherein a second terminal of the second electricallyconductive wire is open circuited, and wherein the heat sensitivematerial is coupled between the first electrically conductive wire andthe second electrically conductive wire.
 12. The foreign objectdetection system of claim 10, wherein a second terminal of the secondelectrically conductive wire is short circuited with the second terminalof the first electrically conductive wire, and wherein at least one ofthe first electrically conductive wire and the second electricallyconductive wire comprises the heat sensitive material.
 13. A foreignobject detection system comprising: a heat sensing system comprising: aninsulation layer including a heat sensitive material having a propertyconfigured to change as a function of temperature, and at least twoelectrically conductive wires; an inductive sensing system comprisingone or more sense coils and at least one of the at least twoelectrically conductive wires, wherein a change in an electricalcharacteristic of the one or more sense coils is indicative of apresence of a foreign object; and a controller coupled to the heatsensing system and the inductive sensing system, the controller beingconfigured to determine that the foreign object is present when both themeasure of the property of the heat sensitive material and the measureof the electrical characteristic of the one or more sense coils indicatethe presence of the foreign object.
 14. A foreign object detectionsystem comprising: a heat sensing system comprising: an insulation layerincluding a heat sensitive material having a property configured tochange as a function of temperature, and at least two electricallyconductive wires; an inductive sensing system comprising one or moresense coils and at least one of the at least two electrically conductivewires, wherein a change in an electrical characteristic of the one ormore sense coils is indicative of a presence of a foreign object; and acontroller coupled to the heat sensing system and the inductive sensingsystem, the controller being configured to control the inductive sensingsystem based on the measure of the property of the heat sensitivematerial by at least: measuring the electrical characteristic of the oneor more sense coils when the measure of the property of the heatsensitive material satisfies a threshold; and determining that theforeign object is present when the measure of the electricalcharacteristic satisfies another threshold.
 15. A foreign objectdetection system comprising: a heat sensing system comprising: aninsulation layer including a heat sensitive material having a propertyconfigured to change as a function of temperature, and at least twoelectrically conductive wires; an inductive sensing system comprisingone or more sense coils and at least one of the at least twoelectrically conductive wires, wherein a change in an electricalcharacteristic of the one or more sense coils is indicative of apresence of a foreign object; and a controller coupled to the heatsensing system and the inductive sensing system, the controller beingconfigured to control the heat sensing system based on the measure ofthe electrical characteristic of the one or more sense coils by atleast: measuring the property of the heat sensitive material when theelectrical characteristic of the one or more sense coils satisfies athreshold; and determine that the foreign object is present when themeasure of the property satisfies another threshold.
 16. A foreignobject detection system comprising: a heat sensing system comprising: aninsulation layer including a heat sensitive material having a propertyconfigured to change as a function of temperature, and at least twoelectrically conductive wires; an inductive sensing system comprisingone or more sense coils and at least one of the at least twoelectrically conductive wires, wherein a change in an electricalcharacteristic of the one or more sense coils is indicative of apresence of a foreign object; and a controller coupled to the heatsensing system and the inductive sensing system, the controller beingconfigured to determine the presence of the foreign object based oncorrelating at least one of the measure of the property of the heatsensitive material and the measure of the electrical characteristic ofthe one or more sense coils with a level of an alternating magneticfield generated by a wireless power transfer pad.
 17. A method forcontrolling a foreign object detection system, the method comprising:determining a change in a property of a heat sensitive material bymeasuring a resistance between at least two electrically conductivewires, the heat sensitive material being coupled between the at leasttwo electrically conductive wires; determining a change in an electricalcharacteristic of one or more sense coils; and determining a presence ofa foreign object based on at least one of the determined change in theproperty of the heat sensitive material or the determined change in theelectrical characteristic of one or more sense coils.
 18. The method ofclaim 17, wherein the one or more sense coils comprise the heatsensitive material.
 19. The method of claim 17, wherein determining thechange in the electrical characteristic of the one or more sense coilscomprises measuring an inductance of at least one of the at least twoelectrically conductive wires.
 20. The method of claim 17, wherein theproperty comprises an electrical conductivity, and wherein determiningthe presence of the foreign object is performed based on the change inthe electrical conductivity satisfying a threshold.
 21. The method ofclaim 17, wherein determining the change in the electricalcharacteristic of the one or more sense coils is based on the change inthe property of the heat sensitive material.
 22. The method of claim 17,wherein determining the change in the property of the heat sensitivematerial is based on the change in the electrical characteristic of theone or more sense coils.
 23. A method for controlling a foreign objectdetection system, the method comprising: determining a change in aproperty of a heat sensitive material; determining a change in anelectrical characteristic of one or more sense coils; determining apresence of a foreign object based on at least one of the determinedchange in the property of the heat sensitive material or the determinedchange in the electrical characteristic of one or more sense coils;wirelessly transferring power at a wireless power transfer pad, the heatsensitive material being positioned near the wireless power transferpad, and the one or more sense coils being positioned near the wirelesspower transfer pad; and adjusting the wirelessly transferring of thepower or generating an alert based on whether or not the presence of theforeign object is detected.
 24. A method for controlling a foreignobject detection system, the method comprising: determining a change ina property of a heat sensitive material by measuring a resistance alongan electrically conductive wire, the electrically conductive wirecomprising the heat sensitive material; determining a change in anelectrical characteristic of one or more sense coils by measuring aninductance of the electrically conductive wire; and determining apresence of a foreign object based on at least one of the determinedchange in the property of the heat sensitive material or the determinedchange in the electrical characteristic of one or more sense coils. 25.A method for controlling a foreign object detection system, the methodcomprising: determining a change in a property of a heat sensitivematerial; determining a change in an electrical characteristic of one ormore sense coils; determining a presence of a foreign object based on:at least one of the determined change in the property of the heatsensitive material or the determined change in the electricalcharacteristic of the one or more sense coils; and correlating the atleast one of the change of the property of the heat sensitive materialor the change of the electrical characteristic of the one or more sensecoils with a level of an alternating magnetic field generated by awireless power transfer pad.